But it was the Federal Reserve that killed the proposal, the official told BuzzFeed, denying a purely political rationale for the announcement, saying the independent central bank would not have credited the Treasury's accounts for the vast sum for depositing the coin.

There are two interesting things about this.

One is that it seems odd that the Fed would decide that there's some legal tender that it will recognize, and some legal tender that it wouldn't recognize.

Furthermore, by placing the blame on the Fed, it would seem that the White House/Treasury wanted to keep this idea available as a last-second escape valve in case things were about to get that bad. Now this option sounds foreclosed to them.